The present invention relates to improvements in picking mechanism for looms, particularly looms of the type which utilize a shuttle box which is rotated 180.degree. before and after each pick such as that illustrated in U.S. Pat. Nos. to V. Svaty 3,315,709 dated Apr. 25, 1967 and 3,330,305 dated July 11, 1967.
Pneumatic picking mechanisms for which the present invention is an improvement generally comprise a picking cylinder and a pump cylinder which are interconnected in a closed pneumatic system. A picking piston is slidable within the picking cylinder and has a picking piston rod which is attached to the picking piston and which extends beyond the picking cylinder for a picking engagement with the shuttle. A pump piston is slidable within the pump cylinder and has attached thereto a pump piston rod which extends beyond the inlet end of the pump cylinder. Mechanical drive means are connected to the extending portion of the pump piston rod for reciprocating the pump piston within the pump cylinder. Conduits connect the inlet end of the picking cylinder to the outlet end of the pump cylinder and the outlet end of the picking cylinder to the inlet end of the pump cylinder in a closed system so that during the power stroke of the pump piston from the inlet to the outlet end of the pump cylinder, air is pumped from the outlet end of the pump cylinder to the inlet end of the picking cylinder thereby driving the picking piston from the inlet end to the outlet end of the picking cylinder in a picking stroke. The extending portion of the picking piston rod engages a shuttle and propels it through the shed to the opposite side of the loom. During this picking stroke, air is forced from the outlet end of the picking cylinder into the inlet end of the pump cylinder thereby assisting the pump piston in its power stroke.
The advantages of a closed pneumatic system such as described above is that much less power is required to reciprocate the pump piston within the pump cylinder. However, certain pressures must be maintained in the picking and pump cylinders during certain phases of each picking cycle. Because of many factors such as heat and loss of air through various seals in the system, the pressures have a tendency to vary from the ideal during certain phases of each cycle. In order to eliminate this problem, it has been common practice to employ bleeder valves at one or both ends of the pump cylinder. These valves are normally closed and are effective when opened to allow air to enter the cylinder when the pressure in the cylinder is less than atmospheric and to allow air to exit from the cylinder if the pressure within the cylinder is greater than atmospheric. Mechanical means are employed to open each bleeder valve at a point during each picking cycle. This occurs at a point in the cycle where the pressure in the portion of the cylinder that is adjacent the bleeder valve is atmospheric when the cylinder is operating under ideal pressures. When the pressures stray from the ideal, the pressure within the portion of the cylinder which is adjacent the bleeder valve will either be above or below atmospheric at the point in the cycle where the valve is opened. At this point, air will be either expelled or taken into the cylinder so that the operating pressures will return to the ideal state. In this way, the system is self correcting during normal operation of the loom.
A problem arises in the above picking systems when the loom is shut down for an extended period of time, as for example, between shifts, or a changing of a warp, or for any other reason. During an extended period of shut down of the loom, a substantial portion of the air may be lost from the picking and pump cylinders thru the various seals throughout the system. When the loom is started, there may not be enough air pressure in the inlet end of the pump cylinder during the return stroke of the pump piston to cause the picking piston to achieve a full return stroke. This means that the picking piston rod will remain outside of the picking cylinder at least to some degree. During the picking stroke of the picking cylinder, the shuttle will not be given a full picking stroke and will either not pass completely through the warp shed or will box improperly on the other side of the loom. In addition, the portion of the picking piston rod which extends from the piston picking cylinder is likely to be damaged by moving parts associated with picking expecially in picking of gripper shuttle looms such as that disclosed in the above-identified U.S. patents which employ a rotatable shuttle box. As the shuttle box is rotated 180.degree., it will strike and damage the extending portion of the picking piston rod. Since the bleeder valves can only be opened for a very short portion of each picking cycle they are not effective to draw in enough air to bring the system back to an ideal pressure situation. If a substantial amount of air is lost during the shut-down period, it may take several picks before the cylinder pressures reach their ideal operating state. During this time, faulty picking will occur and damage will occur to various picking components.